Provenance of the uppermost clastic rocks of the Lower Cretaceous Kezilesu Group from the Ulugqat Basin, Xinjiang, NW China and its tectonic implications: Insights from sedimentary records and detrital zircon U–Pb geochronology

Abstract

The Ulugqat Basin is located at the juncture of the Tarim Basin, the western Tianshan Orogen of the Central Asian Orogenic Belt, and the Pamir salient of the Tethys domain. A comprehensive provenance study using sedimentology, petrology, and detrital zircon U–Pb geochronology was carried out on the clastic rocks of the fifth member of the Lower Cretaceous Kezilesu Group from the Ulugqat Basin, aiming to better understand the nature of its relationships with the neighbouring tectonic units as well as the formation of sandstone‐hosted Zn–Pb mineralization. The fifth member consists of conglomerate, gravelly sandstone, sandstone, and mudstone interbeds, and is interpreted as alluvial fan–braid river–braid river delta sediments. The conglomerate and gravelly sandstone contain different kinds of lithic fragments, including phyllite, quartzite, chert, chalcedony, and some felsic igneous rocks, with low compositional maturities. The detrital zircon U–Pb ages of sandstone from the uppermost part of the fifth member range widely from 229.7 to 2,984.9 Ma, concentratedly distributed in five groups: 230–300, 390–480, 750–880, 1,600–2,200, and 2,300–3,000 Ma. The identified palaeocurrent directions, heavy mineral assemblages, specific provenance indicators, and distributions of detrital zircon U–Pb ages all indicate that these clastic rocks are probably sourced from the South Tianshan Orogen to the north, rather than the Pamir salient, probably involving the Proterozoic Aksu metamorphic rocks, Palaeozoic sedimentary rocks, Late Carboniferous–Early Permian alkali granite, and some mafic/ultramafic rocks of ophiolitic mélange. This interpretation is consistent with a late Early Cretaceous uplifting of the South Tianshan Orogen according to previous low‐temperature thermochronological data sets. The thick deposition of these Lower Cretaceous clastic rocks and associated uplifting of the South Tianshan Orogen are interpreted to be related to the coeval collision of the Karakoram–Lhasa Block with the southern Asian margin.